1. Field of the Invention
The invention is related to the field of wafer process verification, and in particular, to identifying parasitic shunts formed between the shields in read elements in magnetic heads due to problems in the fabrication process.
2. Statement of the Problem
Wafer fabrication is a procedure composed of many repeated sequential processes to produce electrical circuits, devices, components, etc. One type of device formed through wafer fabrication is magnetic heads. Magnetic heads are used to write to magnetic recording disks and to read from magnetic recording disks, such as in a hard disk drive. Magnetic heads typically include a read element and a write element. The structure of a read element includes a first shield, a magnetoresistance (MR) sensor formed on the first shield, and a second shield formed on the MR sensor. The MR sensor may comprise a Giant MR (GMR) sensor, a Tunneling MR (TMR) sensor, or another type of MR sensor. If the read element is being operated in a current perpendicular to plane (CPP) fashion, then the first shield and the second shield are electrically connected to opposing surfaces of the MR sensor to act as current leads for a sense current that is injected perpendicularly through the MR sensor.
One problem encountered when fabricating read elements in magnetic heads is the inadvertent formation of parasitic shunts between the first shield and the second shield. As the bit densities of magnetic disks have increased, the size of the read element on the magnetic head has decreased. Thus, the shields of the read sensor are formed closer together, which increases the chances of inadvertent parasitic shunts forming between the shields during fabrication. Additionally, there are other layers formed between the shields, such as hard bias magnets, that are separated from the shields by a thin insulating material. These areas of a read element are especially susceptible to parasitic shunts. These parasitic shunts, which are formed in parallel with the MR sensor, are not well controlled and may cause yield loss due to large resistance variations. It would therefore be desirable to effectively and efficiently test the quality of the fabrication processes used to form read elements in magnetic heads to identify the parasitic shunts formed.